Electronics Forum / Basics / June 2006

I would say you are not the right person to make this type of selection
(no offence meant.)

 the most common are the NPN no.. (normally opened).
NPN are sinked typed and is generally stated as an
open collector.
  just think of a transistor with the Emitter to common.
collector being the output.
 all you do is simply pull a + source to common with it
which is what most digital input devices are.

  the PNP are source type if you want to look at it that way!
 it really is nothing more than a PNP transistor with its emitter
connected to the High side of the supply and the collector being
the output.
  in general, you sources out the voltage from the high side.
for example.
  PNP (NO normally open) with a Brown, Blue and black wire.
brown mite go to a 10..30 volt DC supply some where, the
blue going to the common of that supply and the black being
the output from the collector of the PNP transistor.,
 when the prox is tripped, you will get on the output what
ever the brown wire supply voltage.

 with NPN, it simply pulls the black wire to common. this also
makes it nice to have the prox operate on lets say 12 volts and
the black wire can pull to common any dc voltage up to the max the
collector can handle which can be higher than what the prox is
using at its brown wire.

 and of course the NC = normally closed and No is normally opened.
like i said, in most cases you want the prox to close when it is
near metal or what ever type your getting, there are cases where
you mite want it to open when its near metal.
 P.S.
  i guess the NEC people have decided to stop using blue as a low
side color and use gray instead. just keep that in mind.

NPN outputs connect to the negative supply rail when on (load is
always connected to positive rail).

PNP outputs connect to the positive supply rail when on (load always
connected to negative rail).

NO (normally open) = output off till metal near.

NC (normally closed) = output on till metal near.